High strength alloy



United States Patent HIGH STRENGTH ALLOY No Drawing. Application May 21, 1957 Serial No. 660,457

-4 Claims. 01. 75-124 The present invention relates to alloys which have high strength at temperatures up to and exceeding 1200 F., have improved tensile properties at room temperature, and which'may be readily formed into wrought articles .as well as sheet. stock material having desirable welding properties.

This application is a continuation-in-part of High Strength Alloy, 1956, now abandoned, by the present inventors and assigned to the assignees of this application.

The development of the gas turbine and similar apparatus has created a demand for materials having higher strength and greater stability at elevated temperatures than the high temperature alloys currently available. Certain components of such apparatus such as turbine buckets and blades are subjected to very high stresses over long periods of time in highly corrosive atmospheres at continuous temperatures of the order of 1500 F. or more. Other components such as the turbine wheel members which support the bucket elements, sheet metal members constituting the tail pipe or cone and the like, are similarly subjected to high stresses and Serial 'No. 588,975, filed on June 4,

corrosive atmospheres at continuous temperatures of the e order of 1200 F. or more.

In general, the articles which must withstand the higher stresses and temperatures as noted above, have been fabricated by either precision casting techniques or have been forged from alloys which are capable of being Worked to final form from castings or ingots. The work'- able alloys of this type have usually been precipitation hardeuable materials and have usually contained substantial amounts of strategic materials such as cobalt and columbium and have usually had as a major con- .stituent, for example, as much as 40 percent or more nickel. These elements are in relatively short supply, are expensive and, further, while these high strength .alloys containing these strategic elements are capable of being Worked to some degree, they are not readily reducible to sheet material by conventional rolling practices. Furthermore, these materials may be welded only with considerable difliculty and usually exhibit a weakened zone at the weld.

Alloys which have been employed as structural elements at about 1200 F. have been lower in strategic element content and have been more readily workable. These materials have usually been modified stainless steels and have been only moderately weldable. In general, the more easily and successfully Weldable materials have had lower mechanical properties such as stress rupture strength and elevated temperature ultimate and yield strengths while those which have had higher mechanical properties, particularly at temperatures of the order of 1200 F. and higher have been more diflicult to work -and have not been as satisfactorily-welded.

Accordingly, a principal object of our invention is the provision of an alloy having high mechanical strength and resistance to corrosion at elevated temperatures which is readily fabricated by forging or rolling and which is readily welded.

A further object of our invention is the provision of such an alloy which is readily reduced by rolling into sheet metal.

Other and specifically diiferent objects of our invention will become apparent to those skilled in the art from the following disclosure.

Briefly stated, in accordance with one aspect of our invention we provide an austenitic alloy consisting essentially of from about 30.0 to 35.0 percent by weight nickel, from about 12 to about 15 percent chromium, from about 5.5 to 7.5 percent tungsten, from about 2.5 to about 5 percent molybdenum, from about 1.5 to about 4.5 perabout 6.0 to 7.0 percent and preferably about 6 percent tungsten, about 3.0 to 4.6 percent and preferably about 3.5 percent molybdenum, about 1.75 to about 2.5 percent and preferably about 2.0 percent titanium, about 0.2 to 0.5 percent and preferably about 0.45 percent aluminum, not more than about 0.4 percent and preferably about 0.35 percent zirconium, no more than and preferably less than about 0.08 percent carbon, and the balance substantially all iron, has high tensile strength and ductillty, high temperature stress rupture strength and duetility, and is readily formed and welded. It will be understood that the phrase balance substantially all iron as used herein includes minor amounts 'of impurities customarily found in ferrous alloys of this type such as, for example, manganese, silicon, sulfur and phosphorus. It has been found that the total of these particular impurities may constitute as much as about 0.2 weight percent of these alloys without impairing their mechanical properties but preferably should not exceed about 0.05 percent manganese, 0.05 percent silicon,

0.04 percent sulfur, and 0.04 percent phosphorus. Of course, other elements may also be present in very small amounts, as is customary. in such materials.

Yet further, we have discovered that substantially the same alloy composition, but one which contains from about 2.5 to 4.5% titanium and particularly from about -3 to 4% titanium, exhibits a higher room temperature tensile strength and yield strength than would be ex- ;pected when compared with the alloys having the lower .discussed in more detail subsequently.

By *way of example, alloys having the following specific compositions were prepared as "stated previously.

Table I Heat N0. N1 01' W Mo T1 Al Zr Fe 32. 9 13. 0 6. 4 3. 1 2. 2 0.35 0. 20 0. 04 42. 0 32.9 13.1 6.7 3.0 1.6 0.39 0.161 0.04 .Bal. 31. 7 14. 7 l6. 8 l 2. 0 2. 1 O. 27 0. 01' 0. 04 '42. 3 :32. 2 12. 8 6.3 3. "2. 1' 0.50 '0. 05 0.10 -B111 32. 5 12. 8 0. 2 3. 5 1. 9 0.39 0. 17 0. 04 -B211.

32.8 12.7 6.1 3.4 2.0 0.31 0.00 "E21. 32. 8 13. 1 6. 0 3. 2 19 0. l5 '0. 00 3211. 32. 2 12. 8 3. 6 1. 9 0.34 r 0510 0. 04 .2801. 32. 4 13. 0 .3. 0 3. 0 1. 9' '0.' 37 0. 05 10106 13211. 32.4 12. 8 6. 1 .3. 4- "'2. 8' 0. 41 0. 05 0.05 Bal.

. 32. 5 '12. 9 6. 1 3. 4 3. 8 0. 43 0.16 006 -Bal.

'Cast ingots from'theseheats werereduced" toround barstock and to' sheet-material by conventional'iforging and rolling procedures. Conventional tensile -testand stress rupture test :specimens were :prepared fronithis material "and heat treated.

Conventional tensile tests were performed on certain 10f these specimens atroom temperature and elevated temperatures. The following data areexemplary ofthe results of'these tests performed'on specimen'spreparerl from 'bar;stock.

Table II Soln Test .2% Y .S.- UltJTens. .Peroent Heat No. Temp. Temp. (p.s.1.) Str. (p.s .i.) -El0ng.

1 F.) F.) (1":ga.)

- RT 119,000 178,000 24.0 1 2100 1,350 100,000 117,000 21.0 RT 115,800 177,800 5 23.0 :2 1,900 1, 200 104,200 135,500 230 1,350 95, 400 107,500 25.5 RT 129, 100 187,700 18. 5 3 1, 850 1, 200 110, 800 143, 900 319. 0 1,850 93,100 111, 400 18. 5 4 RT 107,800 179,500 23.0 4 1, 950 1, 200 105,000 144,100 21.0 1,350 101,400 114,800 20.0 1 850 RT 138,000 178,000 :1720 5 1,350 96,000 115,000 "19. 0 2 150 RT 93,000 155,000 17.0 1, 350 74, 000 '104, 000 15.0 1 850 RT 117,000 171,000 21..0 6 1, 350 88, 000 104, 000 15. 0 2 150 RT 98,000 159, 000 "20.0 1, 350 ,000 105, 000 1 5. 2 1, 850 RT 114, 000 165000 22.0 7 1, 350 84, 000 102, 000 23. 0 2 150 RT 104,000 150,000 10.0 1, 350 75,000 99, 000 18.0 1 850 RT 110,000 100,000 2550 S 1, 350 77, 000 89, 000 19; 0 2 150 RT 105,000 144,000 12.0 1,350 ,000' 15.0 1 850 RT 109,000 162,000 23.0 g 1, 350 B1, 000 000 15. 0 2 150 RI 100,000 148,000 15.0 1,350 77,000 100,000 :0 1 850 RT 168,000 213,000 10.0 10 1, 350 106, 000 129,000 14.0 2 150 RT 103,000 158,000 12.0 1, 350 91, 000 111, 000 5.7 1 850 RT 191,000 223,000 3.4 n p 1, 350 103, 000 127, 000 16. 0 150 RT 130,000 161,000 2.7 1, 350 121,000 124,000 0.8

' Specimen broke in clamp or-on gauge marks.

The test results givenabove were obtained-fromspecimens .given the following .heat treatments. Heat .1 specimens were solution treated by heating at .2000? F. .for 4 hours, oil quenched and aged at 1350 F. 011.24 hours and air cooled. Heat 2 specimens were heatedat .1900 F. for 4 hours, oil quenchedandaged at.l350F. for 24 hours and air cooled. Heat 3 specimens were heated at 1850 F. for 1 hour, oil quenched and aged at 1350 F for 24. hours and air cooled. "Heat 4' speci menswere heated at 1950 F. for 1 hour, oil quenched and aged at 1350 F.for 24 hoursand air cooled; "Heats "5 to 11 weresolution treated by heatattheindicated temperatures for 1 hour, oil quenchedanda'gedM 1550 F. for-'24 hours and air-cooled.

these tests performed upon specimens prepared from sheet stock.

' "1110 test speeimensfrommeat 2 were cut"from 0.062 inch thick sheet stock parallel to the rolling direction, heated for 120 .:-jminutes-.in a protective atmosphere at 1850 F., air cooledrandzaged at.l'350 F. for 24 hours followed by aircooling. The test specimens from heat 3 were cut from 0.064 inch thieksheet stock transverse to the rolling direction, heated for minutes in a protective atmosphere at 1900 F., air cooled and aged at 1350 0024 hours, followed byaircooling.

Conventional stress rupture tests were-performed upon certain others ofthese'specimens at elevated temperatures. The "following 'dataare "exemplary of "the results ofthese tests performed uponspecimens prepared from banstock.

Table IV Boln Test Elongation HeatNo. 'Temp,, Temp., Load Life (1" gage F. F. (p.s.i.) (hi-s.) length), 1 Percent 1,350 50,000 307 1 2,150 1,350 50,000 343 7.0 "1'03 32'888 i3. 318 2 11850 1,350 03,000 4 32.0 1, 350 45. 000 47 4s. 0 1323 30838 3'8 3 5 21000 1,350 55,000 120 22.0 1,350 45,000 404 2&0 1, 200V 87, 000 200 12. 0 4 .2050 1,350 55,000 124 12.0 -1, 350 55, 000 129 10. 0 1, 850 1, 350 50, 000 72 14. 0 1, 200 00, 000 19 7. 2 2,150 1, 350 50,000 210 0. 3 1, 500 25, 000 10s 29. 0 1, s50 1, 350 50, 000 75 32. 0 0 1,200 90, 000 101 8. 0 2,150 1, 350 50,000 188 10'. 0 1, 500 25, 000 87 30. 0 1,550 1,350 50,000 114 18.0 7 1, 200 90, 000 151 15; 0 2, 150 1, 350 50, 000 231 15. 0 1,500 25,000 102 28.0 1, 350 1, 350 50, 000 17 21. 0 s 1, 200 90, 000 6 0. 7 2, 150 1, 350 50, 000 54 1s. 0 1, 500 25, 000 25 32. 0 1,850 1,350 50,000 58 24.0 9 1,200 90,000 7s 3.9 2, 150 1, 350 50,000 95 15. 0 1, 500 25,000 75 24. 0 x 1,850 1,350 50,000 16.0 10 1, 200 90, 000 270 2. 2 2,150 1,350 50,000 816 3.6 1, 500 25,000 181 :13. 0 1,850 1, 350 50; 000 81 10. 0 11 1; 200 90,0 2 0. 65 1.0 2,150 1,350 50,000 361 2.4 1,500 25,000 200 11. 0

{Temperature dropped to 1,l60 F. during test. 2 1 Broke in fillet.

The following dataareexemplary of-wthc= results-tot 75 3 were heated .at'2.000..F.- for.l..hour, ..oil quenchediand mosses aged at 1350" F. for 24 hours and air cooled. The above specimens from heat 4 were heated at 2050 F. for 1 hour, oil quenched and aged at 1350" F. for 24 hours and air cooled. The above specimens from heats 5 to 11 were solution treated by heating at the indicated temperatures for one hour, oil quenched and aged at 1350" F. for 24 hours and air cooled.

The following data are exemplary of the results of these tests performed upon specimens prepared from sheet stock.

Table V Test Elongation Heat N 0. Temp., Load Life (1" ga e F. (p.s.i.) (hrs.) length Percent 1 Test discontinued, specimen unbroken.

The above specimens from heat 2 were cut from 0.062 inch thick sheet stock parallel to the rolling direction and were heated in a protective atmosphere at 2000 F. for 20 minutes, air cooled and aged at 1350 F. for 24 hours followed by air cooling. The above specimens from heat 3 were cut from 0.064 inch thick sheet stock transverse to the rolling direction and were heat treated in a protective atmosphere at 2000 F. for 30 minutes, air cooled and aged at 1350 F. for 24 hours followed by air cooling.

From these and other test data, it was determined that the mechanical properties of the alloy of our invention varies to an unexpected great degree in response to quite small changes in composition and to the temperature at which the solution heat treatment is accomplished. For example, with regard to room temperature tensile properties, it will be noted that in all the heats, the highest yield and ultimate tensile strengths are attained by solu tion heat treating at 1850" F. Further, that while the omission of the small amounts of aluminum and zirconium produced a significant decrease in these properties in the 1850 F. solution treated material and a relatively small increase in these properties in the 2150 F. solution treated material, yet these increased room temperature yield and ultimate tensile strengths were still inferior to alloys containing these small additions and treated at 1850 F. and to the alloys without the additions which were treated at 1850 F. Similar results were obtained when the tungsten content was eliminated and also when it was significantly reduced.

When the titanium content was increased from about 2% to 3% the material solution treated at 1850 F. exhibited about a 2030% increase in room temperature yield strength and about a 13 to 20% increase in room temperature ultimate tensile strength. The corresponding material treated at 2150 F. however did not exhibit as high an increase in these properties. When, however, the titanium content was increased to 4%, both the material solution treated at 1850 F. and the 2150" F. showed a remarkable increase in these properties.

On the other hand, much higher elevated temperature stress rupture strengths are exhibited by the alloy of our invention when the solution heat treatment is accomplished at temperatures above 1850 F. and particularly when treated at 2150 F. as shown. It will therefore be apparent that if the alloy of our invention is to be used as a structural material in high temperature environments, the optimum mechanical properties are attained by solution heat treating at about 2150 F. and aging at about 1350 F. and alloy consisting essentially of from about 30 to 35% nickel, from about 12 to 15% chromium, from about 5.5 to 7.5% tungsten, from about 2.5 to 5% molybdenum, from about 1.5 to 2.5% tita nium, up to about 0.50% aluminum, up to about 0.50% zirconium, up to about 0.1% carbon and balance substantially all iron with no more than the previously noted amounts of impurities. If, however, high room temperature mechanical properties are desired, the titanium content of the alloy should be increased to the range 2.5 to about 4.5% titanium and the solution heat treatment should be decreased to about 1850 F. and the material aged at about 1350 F. As shown, it may therefore be seen that the alloy of our invention, at room temperature, exhibits an ultimate tensile strength of up to about 220,000 p.s.i. or higher, a 0.2 percent ofiset yield strength of about 190,000 p.s.i. or higher, and the ductility is from about 3.5 to 24 percent elongation. At 1350 F. the ultimate tensile strength is up to about 129,000 p.s.i. the 0.2 percent ofiset yield strength is about l00,000.p.s.i. or higher, and the ductility is from about 1 to 25 percent elongation.-

. The stres's rupture tests indicate by extrapolation that the alloys of our invention will Withstand a continuously applied load of about 76,000 p.s.i. for 1000 hours at 1200? F. and a'continuously applied load of about 41,000

I p.s.i. for 1000 hours at 1350 F. before fracturing.

' In comparison with previously known alloys having similar compositions, one such commercially available alloy having the composition of about 44 percent nickel, 34.5 percent iron, 12.8 percent chromium, 5.7 percent molybdenum, 2.4 percent titanium, 0.45 percent manganese, 0.23 percent silicon, 0.03 percent copper, 0.01 percent sulfur, and 0.04 percent carbon has been found to have the following mechanical properties.

Table VI Testing Temperatures F.)

Room 1,200 F. 1,350" F. Temp.

Ult. Tens. Str p.s.i.. 174,000 135, 000 102, 000 0.2% Yield Str 102, 000 98, 000 82, 000 Percent Elongation 19 20 11 Bar stock specimens of this material have been found to have a 1000 hour stress rupture strength of about 55,000 p.s.i. at 1200" F., and a 1000 hour stress rupture strength of about 30,000 p.s.i. at 1350 F.

Another similar commercially available alloy consisting essentially of 26' percent nickel, 15 percent chromium, 1.5 percent molybdenum, 1.6 percent titanium, 0.17 percent aluminum, 0.2 percent vanadium, 0.05 percent carbon, and the balance substantially all iron, has been found to have the following mechanical properties.

Table VII Testing Temperatures F.)

Room 1,200 F. 1,350 F. Temp.

Ult. Tens. St! p.S.i 157,000 110, 000 74, 000 0.2% Yield Str 98, 000 93, 000 68, 000 Percent Elongation 25 10 10 =7 w l ed j ints r tainin th ir r ngthn t l y- In addi ie lbei g; us n tie. th oy of o r en ni highlyresi stantlo corrosion at elevated temperatures- While w.e have, discussedcertain specific'heat treating schedules in the foregoing. specification for purposes of rendering a,morecomplete disclosure, we do not wish our invention to-.b.e limited to anyparticular treatment or composition except as defined in the appended claims.

What we claim as new anddesire to secure by Letters Patent of the United States is:

1.,An alloy consisting essentiallyof from about-30 to 35 percent byv weight nickel, from about 12 to 15 perecentchromium, fromabout 5.5 to 7.5- percent tangsten, from. about. 2.5 to 5.0 percent, molybdenum, from about 1.5 to 4.5 percent titanium, up,;to about 0.50. per.- cent from 0.01 to about 0.50 percent zire conium, up toabout OLIQ-percentcarbon and the balance, substantially all;iron.

2. An alloy consisting essentially offromabout 31.0 to 34..percent byweight nickel, about,12.5 to 150 percent chromium, about. 6.0 to 7.0 percent tungsten, about 3.0 to 4.6 percent molybdenum, about 1.50 to. 2.5 percent titanium, about 0.2 to 0.5. percent aluminum, from 0.01 to about 0.4 percentzirconium, not more than 0,08 perent carbon,- 7 balance ubstan ly l n a d. no. mo

than 0.2 tot al weight percent. ofmanganese, silicon, sul: u andphosph rus- 3. An ;alloy. consisting essentially of about 33 percent bynweight nickel, about 13 percentchromiuni, about 6. prcen ngs c u 5 p rc tm lybdenum, a o

2.0 percent titanium, about 0.45 percent aluminum,about 0.35 percent zirconium, less than about 0.08. percent car hon, not more thanabout 0.05 percent manganese, ,not more than about 0.05 percent silicon, not more than about 0.04percent sulfur, not more than about 0.04 percent phosphorus and the balance substantially all iron.

4. An alloy consisting essentially of from about 31 to 34% by weight nickel, about 12.5 to 15.0% chromium, about 6.0 to .7.0% tungsten, about 3.0 to 4.6% molybdenum, about 2.5 to 4.5% titanium, about 02 to 0.5% aluminum, from 0.01 to about 0.4% zirconium, not more than 0.08% carbon, balance substantially all iron and noniore than 0.2 total weightrpercent of manganese; silicon, sulfur. and phosphorus.;.

Lohr July 14, 1936 Franks et'al Dec. 16,1947 

1. AN ALLOY CONSISTING ESSENTIALLY OF FROM ABOUT 30 TO 35 PERCENT BY WEIGHT NICKEL, FROM ABOUT 12 TO 15 PERCENT CHROMIUM FROM ABOUT 5.5 TO 7.5 PERCENT TUNGSTEN, FROM ABOUT 2.5 TO 5.0 PERCENT MOLYBDENUM, FROM ABOUT 1.5 TO 4.5 PERCENT TITANIUM UP TO ABOUT 0.05 PERCENT ALUMINUM, FROM 0.01 TO ABOUT 0.50 PERCENT ZIRCONIUM, UP TO ABOUT 0.01 PERCENT CARBON AND THE BALANCE SUBSTANTIALLY ALL IRON. 